The disclosures herein relate generally to heat dissipation and more particularly to a system for providing heat dissipation for integrated circuits in a portable computer system.
A portable computer is a self-contained personal computer which can be easily moved to and operated at various locations. Portable computers are often referred to as laptop or notebook computers. To be portable, these computers must be small, compact, and lightweight. The conventional portable computer includes a base portion and a lid portion that pivotally opens from the base portion when the portable computer is in use. The lid portion contains a flat panel display such as a liquid crystal display (LCD) or other suitable display.
Heat distribution is a problem with some computers, especially with portable computers. In the past, portable computers have used thermal transfer mechanisms such as heat spreaders, heat sinks, heat pipes, and fans to address this problem. One type of heat spreader is a metal piece that is thermally coupled to a processor and distributes heat away from the processor. Typically, a heat spreader is made of relatively pure aluminum for good thermal conductivity and for reduced weight. However, aluminum oxide coatings typically form on the outside of items made of aluminum which reduces their ability to provide low impedance electrical connections with other items in contact with the aluminum material. Because heat spreaders typically serve only one function, they add extra pieces to the computer system assembly as well as increasing the complexity of the build and repair operations.
Fans and heat sinks provide cost effective mechanisms for thermally managing many types of portable computer systems. Fans, however, require power and heat sinks require space. While power and space are generally in abundant supply in desktop-type minicomputers, portable computers have only a limited supply of both power and space. A commercial advantage is achieved by manufacturing portable computers that are both small and lightweight. Further, portable computers must operate with power conservation in mind. An operable fan may unduly draw upon the batteries of a laptop making it unattractive for long periods of battery-operated use.
Heat pipes are self contained, phase transformation, heat carrying devices, i.e. a superconductor of heat. A typical heat pipe may comprise a closed copper tube having a partial vacuum internally. Water in a hot portion of the tube boils at a lower than usual temperature in the partial vacuum. The boiling water seeks a cooler spot and thus steam moves to carry heat to the cooler spot where the steam condenses to cooler water which returns to the hot spot. The cycle is ongoing which provides a contained circulating system.
U.S. Pat. No. 4,675,783 discloses a heat pipe-heat sink for air cooling of semiconductor devices characterized by arranging heat pipes in a zig-zag form toward the direction of air flow around the fin section in the heat sinks. A block for mounting the semiconductor device is fitted to the heat-in sections of the plural heat pipes arranged in parallel, and a large number of radiating fins crossing over the heat pipes are fitted to the heat-out sections of the heat pipes protruding from the block.
U.S. Pat. No. 5,568,360 discloses a heat transfer system provided for dissipating thermal energy within a personal computer. The transfer system is designed to move heat from a heat source, such as a central processing unit (CPU), to a heat sink arranged upon the portable computer keyboard. The heat transfer mechanism includes a heat slug thermally coupled to the CPU heat source, and a heat pipe thermally coupled to a backside surface of a computer keyboard. The heat pipe is designed having minimal thermal gradient, and includes an evaporation/condensation cycle associated with its operation. The heat pipe is preferably orthogonally shaped having at least one flat surface arranged near the intersection of the orthogonal members. The flat section is in registry with a heat source. Movement of the flat section relative to the heat source effectuates abutment and thermal contact therebetween. This thermal energy transfer system is designed for enhanced heat transfer within a portable computer system without undergoing the disadvantages of bulky finned heat sinks and/or fans.
U.S. Pat. No. 5,598,320 discloses a rotatable and slidable heat pipe apparatus for transferring heat away from a microprocessor chip more rapidly than by heat sink surface area dissipation to the surrounding air alone, comprising a heat sink with an integral cylindrical passageway adapted to receive a first end of a heat pipe shaped like a crankshaft, and a heat spreader formed from a metal plate with a first end rolled up to define a cylindrical opening adapted to receive a second end of the heat pipe. The heat spreader is attached to an underside of a keyboard. Since the heat pipe is able to rotate within the cylindrical passageway and the cylindrical opening, the keyboard can be raised to an open position and lowered to a closed position quickly and simply without the risk of breaking or bending the heat pipe, and manufacturing position tolerances between the heat pipe apparatus components are increased resulting in a simplified manufacturing process. The heat pipe can also be slid in to and out of the cylindrical passageway or the cylindrical opening, thereby enabling computer manufacturers to incorporate the heat pipe into portable battery powered notebook-type computer systems designed to allow a user to remove, replace, or swap internal components by simply flipping open or removing the keyboard, and further enabling a user to perform maintenance work or repairs on the computer system without concern for damage to the heat pipe.
U.S. Pat. No. 5,764,482 discloses a heat sink for an integrated circuit chip which uses heat pipe cooling to remove the heat. The heat sink is a heat conductive structure such as a bowl which is associated with the integrated circuit socket, having the heat conductive structure held against the integrated circuit. A heat pipe is attached to the structure by using an extension from the heat conductive structure and wrapping the extension around a simple cylindrical heat pipe. One embodiment uses spring clips to attach the heat sink to the socket, and another version uses attachment screws through tabs which are formed from the material around a bowl shaped heat conductive structure.
Processor modules require an efficient and effective thermal connection to insure that a proper operating temperature is maintained during use. It is desirable to install the processor late in the assembly process in order to support order requirements. Because the heat transfer assembly is installed prior to the processor module, a problem arises. The heat transfer assembly includes a heat sink coupled to a heat pipe. The heat pipe extends from the heat sink to a position of engagement with a top surface of the processor module. Due to the rigid structure of the heat pipe, the processor module cannot be installed when the heat transfer assembly is in place. Thus, the heat transfer assembly must be removed, or at least disconnected from the chassis to permit installation of the processor module.
Therefore, what is needed is a heat transfer assembly which can be installed in a portable computer chassis prior to the installation of the processor module, and which does not require removal or disconnection from the chassis to permit the processor module to be installed.